# Marker-assisted selection

> Marker-assisted selection is choosing seedlings or parents by testing DNA markers linked to wanted traits, so plants can be selected before they flower.

- Canonical: https://genetixbay.com/knowledge/glossary/marker-assisted-selection.html
- Also written: MAS, marker assisted selection, marker-assisted breeding, molecular breeding, genomic selection
- Glossary category: Genetics and breeding · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Marker-assisted selection (MAS) uses DNA markers tightly linked to a trait to decide which plants to keep, rather than waiting for the trait to show. A leaf punch from a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) is tested, and only plants carrying the wanted marker [alleles](https://genetixbay.com/knowledge/glossary/allele.md) are grown on. Genomic selection extends the idea to many markers at once for [quantitative traits](https://genetixbay.com/knowledge/glossary/quantitative-trait.md).

## In practice

The most useful cannabis markers so far are for traits with simple genetics: sex (a Y-linked marker), [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase type, and major flowering-time loci such as Autoflower1 (Toth et al. 2020; Toth et al. 2022). Screening 200 seedlings for sex and chemotype in week two saves months of space compared with growing them all to flower.

MAS is weaker for complex traits like yield, [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) or [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md), where many genes each contribute a little and the environment adds noise. It also depends on [linkage](https://genetixbay.com/knowledge/glossary/linkage.md): if the marker is not inside the gene, recombination can break the association in some offspring.

## Don't confuse with

- **Genetic engineering**: MAS selects among natural variation; it does not change DNA.
- **Genotyping for identity**: the same tools, used to compare plants rather than to select.

## Related terms

[Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md), [SNP](https://genetixbay.com/knowledge/glossary/snp.md), [QTL](https://genetixbay.com/knowledge/glossary/qtl.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md)

## Read more

- [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md)

## Sources

1. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667
2. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680
3. Barcaccia G, Palumbo F, Scariolo F, Vannozzi A, Borin M, Bona S. 2020. Potentials and challenges of genomics for breeding cannabis cultivars. Frontiers in Plant Science 11:573299. https://doi.org/10.3389/fpls.2020.573299